In a culture that's "acidic" and "corrosive," Pastor Tim Keller acknowledged that it's hard for Christians not to be negatively influenced particularly when it comes to views on marriage and divorce.

Speaking on the Focus on the Family radio program Tuesday, Keller tried to give Christians the benefit of the doubt when analyzing the high divorce rate among believers.

"If you go out in the rain even if you have an umbrella on or a raincoat, you're still going to get pretty wet, fairly wet, somewhat," the Redeemer Presbyterian Church pastor illustrated.

"If two Christians get married, both of them have to swim against the tide of the culture. If one of them does and one of them doesn't it still may end up in divorce. It's not all that surprising then that we are getting wet."

Christians, nevertheless, are doing better than the culture when it comes to intact marriages, Keller noted. "But at the same time, we are living in a very acidic, corrosive place. It's really tough. There's pornography thrown at you. There's the popular culture you get through TV and movies."

The culture ultimately "undercuts what you are reading in the Bible," the influential pastor lamented.

But Keller's wife, Kathy was not content to give people a pass. She said on the radio program that the real problem of divorce stems from "Christians not understanding how Christianity works."

"People who call themselves committed Christians may be assenting to certain truths without ever having taken the Gospel in as the center that energizes their whole life," she said.

"Unless you do that – meaning my life is laid down for you in the imitation of what Christ did – then you're operating out of a very self-serving template when you get into a relationship."

In studying gender roles, and in writing their new book, The Meaning of Marriage: Facing the Complexities of Commitment with the Wisdom of God, Kathy Keller said that both the husband and the wife are to take on the role of Jesus in the marriage – with the husband dying to himself to sanctify his wife, and the wife taking on the role of Jesus as a servant.

When the Gospel isn't in the center of a relationship, that's when you have problems, she summed. She said from the very beginning humans are all about looking out for number one. And fighting the "me" mentality is hard work.

But both Kellers agreed there are ways to fight it and make a marriage stronger. Pastor Keller said that the biggest way is by identifying ways you are being self-centered in the marriage rather than serving the other person.

He spoke candidly about some of his own struggles saying that one of his biggest sins is "trying to make myself impervious to people's criticisms by working so hard, I overwork, so if anyone says anything to me I can say you don't understand how hard I work."

He said he and his wife, after many years and discussions, have identified that as his main struggle – "its selfish servanthood."

But because his wife was able to identify the problem and call him out on it, they were able to make breakthroughs in their marriage.

Kathy Keller compared this problem solving method to that of a "player-coach." She said she and her husband are like two players on a field, but if they are having a disagreement or one of them is doing something wrong, the other one has to take on the role of a coach and blow the whistle. They then have to step off the field and figure out what is going wrong.

This kind of vulnerability and understanding takes years to achieve, she said, but husbands and wives are meant to be "vehicles of sanctification in each other's lives."

The three-part marriage series continues through Wednesday on Focus on the Family. The series is exploring a biblically-rooted understanding of God's design for marriage. Earlier, the Kellers discussed the idea of a "consumer mentality" that has taken hold of the landscape of relationships and marriage, making it easy for people to walk away.